Not Applicable
Not Applicable
Not Applicable
The present invention relates to a rotary blower, such as a supercharger for supercharging an internal combustion engine. More particularly, the invention relates to a supercharger having a fluid pressure operated clutch assembly adapted to transmit torque from an input to the supercharger rotors.
Although the present invention may be used advantageously with superchargers having various rotor types and configurations, such as the male and female rotors found in screw compressors, it has been developed for use with a Roots Blower supercharger, and will be described in connection therewith.
As is well known to those skilled in the art, the use of a supercharger to increase or xe2x80x9cboostxe2x80x9d the air pressure in the intake manifold of an internal combustion engine results in an engine having greater horsepower output capability than would occur if the engine were normally aspirated, (i.e., if the piston would draw air into the cylinder during the intake stroke of the piston). However, the conventional supercharger is mechanically driven by the engine, and therefore, represents a drain on engine horsepower whenever engine boost is not required. For the above and other reasons, it has been known for several years to provide some sort of engageable/disengageable clutch assembly disposed in series between the input (e.g., a belt driven pulley) and the blower rotors.
The assignee of the present invention has sold superchargers commercially including such clutch assemblies which operate electromagnetically. Unfortunately, the ON-OFF characteristics of electromagnetic clutches produce a transient load torque on the engine. For example, as the electromagnetic clutch is engaged, the result will be a xe2x80x9cdroopxe2x80x9d in engine speed which will likely be perceived by the driver and maybe manifested as an undesirable slowing down of the vehicle.
It is also known to provide a fluid pressure operated clutch assembly in which the clutch pack is spring biased toward a disengaged condition, and is moved toward an engaged condition in response to axial movement of a fluid pressure actuated piston member. In other words, the known supercharger clutch is of the xe2x80x9cpressure-applied, spring-releasedxe2x80x9d type. Although a supercharger with such a clutch arrangement can operate in a generally satisfactory manner, once the clutch is in either the engaged or the disengaged condition, the known arrangement does involve certain disadvantages during xe2x80x9ctransientxe2x80x9d conditions, i.e., as the clutch assembly changes from the disengaged condition to the engaged condition, or vice versa. By way of example, a known supercharger clutch assembly of the pressure applied, spring released type requires a fairly long piston travel in order to achieve engagement of the clutch pack (or very high apply pressure), thus requiring substantial flow of fluid to accomplish the required piston movement.
Although such a high flow requirement is not a problem, once the engine has reached normal operating temperature, it frequently occurs that engagement of the clutch assembly is required soon after xe2x80x9ccold engine start upxe2x80x9d, while the engine oil is still cold. As a result, the known pressure applied, spring released system will have substantially longer time of engagement when the engine is cold than when the engine is warm, By way of example only, a typical engagement or release response time, as specified by the vehicle manufacturer, would be in the range of about 0.10 seconds. A substantially longer response time would result in the well known xe2x80x9cturbo lagxe2x80x9d feeling wherein the operator depresses the accelerator, but then there is a time lag before engine boost becomes noticeable, as is inherent in a turbo-charger type of engine boost system. On the other hand, response time should not be so fast (when engaging) and so sudden as to result in a large torque spike being imposed upon the engine.
Another disadvantage associated with the pressure-applied type of supercharger clutch is that the oil pressure typically used is the engine lubrication oil circuit. As a result, the fluid pressure available to engage the clutch may be only in the range of about 20 psi., and even that very low pressure may not be available on a sufficiently consistent and predictable basis to be relied upon for engagement of the supercharger clutch, especially within the specified response time.
Accordingly, it is an object of the present invention to provide an improved supercharger and clutch assembly which overcome the above-described disadvantages of the prior art.
It is a more specific object of the present invention to provide an improved supercharger and clutch assembly which accomplishes the above-stated object, and which has both a variable and a controllable engagement and disengagement response time, thus avoiding both transient overloading of the engine and a time lag upon engagement.
It is a further object of the present invention to provide such an improved supercharger and clutch assembly which operates in a consistent manner, substantially independent of variables such as engine oil temperature.
The above and other objects of the invention are accomplished by an improved rotary blower of either the backflow or compression type comprising a housing assembly including a main housing and a clutch housing, the main housing defining a blower chamber. Blower rotor assemblies are disposed in the blower chamber for effecting transfer of volumes of fluid in response to rotation of an input shaft. One of the blower rotor assemblies is operably mounted on a rotor shaft and has an input hub portion disposed adjacent the input shaft. A clutch assembly is disposed in the clutch housing and in driven relationship with the input shaft, and in driving relationship with the input hub portion, the clutch assembly being selectively operable between an engaged condition, operable to transmit torque from the input shaft to the input hub portion, and a disengaged condition.
The improved rotary blower is characterized by the clutch assembly including a first set of clutch disks fixed for rotation with the input shaft and a second set of clutch disks fixed for rotation with the input hub portion. A biasing means normally biases the first and second sets of clutch disks toward the engaged condition. A piston member cooperates with the clutch housing to define a pressure chamber, the piston member being axially moveable, in response to the presence of relatively high pressure fluid in the pressure chamber to a position releasing the biasing means and permitting the clutch assembly to move to the disengaged position. A valve means is operably associated with the clutch housing and is operable to communicate the pressure chamber to a source of relatively low pressure fluid in response to an electrical input signal having a first condition, and to a source of relatively high pressure fluid in response to the electrical input signal having a second condition.